The long range objective of this study is to gain insight into the mechanisms of pathogenesis of Chlamydiae. A current hypothesis is that there are special phylogenetic structure(s) responsible for (1) attachment/entry of susceptible cells, (2) initiation and maintenance of intracellular survival in both professional and non-professional phagocytic cells, and (3) immediate cytotoxicity. One specific aim of this proposal is to determine if the virulence factor(s) responsible for these biological events are located specifically on the elementary body envelope. The basic approach examines the interaction of isolated, purified radiolabeled elementary body envelopes, alone or coated onto latex spheres, with macrophages and mouse L-cells. A second specific aim is to expand our studies of the in vitro interaction of Chlamydiae with professional phagocyte cells and look at both the in vitro and in vivo effects of these intracellular pathogens on various cells of the immune response. Mitogen induced blastogenic transformation of lymphocytes is being used as the initial index of differences between cells from Chlamydiae infected mice versus cells from L-cell infected controls.